The U.S. House of Representatives has passed a bill that would allow mobile phone users to unlock their devices and switch carriers, overriding a 2013 decision by the Library of Congress to make the practice illegal.

After the bill passed through the House Judiciary Committee, sponsors added language that would allow a prohibition on bulk unlocking of phones to remain in effect. Critics of the added language said it weakened the consumer protections in the bill and would prohibit a legitimate business model of reselling used phones.

The bill was already a "weak" one before the added language, said Sina Khanifar, an activist and former phone unlocker who campaigned for Congress to overturn the Library of Congress' decision to prohibit unlocking. In January 2013, the Library of Congress, reviewing circumvention exceptions allowed under the Digital Millennium Copyright Act (DMCA), allowed a legal exemption for unlocking a mobile phone to expire.

The Unlocking Consumer Choice Act didn't permanently amend the DMCA to allow mobile phone unlocking, unlike some other proposals, but will allow the Library of Congress to again review the issue in 18 months, Khanifar wrote in a blog post.

The new language, excluding bulk unlocking from the legal exemption, further weakened the bill, he added. "Bulk unlockers buy phones from a variety of sources, including second-hand devices, unlock and resell them," he wrote. "They're an important part of the electronics recycling and refurbishing industry."

The bulk unlocking provision "sets a very dangerous precedent. It says that Congress is okay with companies using ... the DMCA to prevent certain business models, even when they have absolutely nothing to do with copyright infringement," he added.

Still, the bill had support from several groups including mobile phone trade group CTIA, Consumers Union and the Fraternal Order of Police, noted Representative Bob Goodlatte, a Virginia Republican and the bill's main sponsor. The bulk unlocking provision was added to address police concerns about stolen mobile phones, a House staffer said.

The bill "protects consumer choice by allowing consumers flexibility when it comes to choosing a wireless carrier," he said in a statement. "This is something that Americans have been asking for and I am pleased that the House of Representatives acted to restore the exemption that will allow consumers to unlock their cell phones."

Public Knowledge, a digital rights group, said it was disappointed in the new language on bulk unlocking. "It's clear that more needs to be doneA to prevent copyright law from interfering with consumers' rights and picking winners and losers between business models," Sherwin Siy, the group's vice president of legal affairs, said by email.

Grant Gross covers technology and telecom policy in the U.S. government for The IDG News Service. Follow Grant on Twitter at GrantGross. Grant's email address is grant_gross@idg.com.